Mask Making Decision for Manufacturing (DFM) on Mask Quality Control

ABSTRACT

The present disclosure provide a method for making a mask. The method includes assigning a plurality of pattern features to different data types; writing the plurality of pattern features on a mask; inspecting the plurality of pattern features with different inspection sensitivities according to assigned data types; and repairing the plurality of pattern features on the mask according to the inspecting of the plurality of pattern features.

BACKGROUND

In semiconductor technologies, a plurality of photomasks (masks) areformed with predesigned integrated circuit (IC) patterns. The pluralityof masks are used to transfer those predesigned IC patterns to multiplesemiconductor wafers in lithography processes. The predesigned ICpatterns formed on masks are master patterns. Any defect on a photomaskwill be transferred to multiple semiconductor wafers and cause yieldissues. Therefore, the fabrication of a mask utilizes a high precisionprocess. Further inspection and follow-up repair are also implemented toensure that each mask is fabricated with high quality. However, variouspattern features formed on a mask are designed for different functions.Existing practices on inspection and repairing of a mask can be overlystringent and lead to relatively low throughput and high manufacturingcost.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flowchart of a method to make a mask according to oneembodiment.

FIGS. 2 a and 2 b are top views of a mask constructed according toaspects of the present disclosure in various embodiments.

FIGS. 3 a and 3 b are top views of mask patterns constructed accordingto aspects of the present disclosure in various embodiments.

FIG. 3 c is an exemplary diagram of critical dimension (CD) as comparedto dosage.

FIG. 4 is a block diagram of an exemplary multi-sensitivity inspectionprocess constructed according to aspects of the present disclosure inone embodiment.

FIG. 5 is a top view of an exemplary mask pattern constructed accordingto aspects of the present disclosure in one embodiment.

FIGS. 6 a-6 d are top views of an exemplary mask pattern constructedaccording to aspects of the present disclosure in one embodiment.

FIGS. 7 a-7 b are top views of an exemplary mask pattern constructedaccording to aspects of the present disclosure in one embodiment.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 is a flowchart of one embodiment of a method 100 which can beused to make a photomask (mask, or reticle, collectively referred to asmask). The method 100 is described below with additional reference toFIGS. 1 to 7, which shows a mask being constructed according to aspectsof the present disclosure.

The method 100 begins at step 112 by writing a plurality of patternfeatures on a mask such as a mask 200, as illustrated in FIG. 2 a. Themask 200 includes a transparent substrate 210 in one embodiment. Thetransparent substrate 210 may include fused silica (SiO₂), calciumfluoride (CaF₂), and/or other suitable materials. In the presentembodiment, the mask substrate includes a fused quartz. A mask patternis written on the transparent substrate. The mask pattern includes aplurality of pattern features such as those shown in FIGS. 2 a and 2 b.The mask pattern includes geometries of an integrated circuit pattern tobe formed on a substrate such as a semiconductor wafer. In oneembodiment, the mask includes an integrated circuit feature 212 as shownin FIG. 2 a.

The mask pattern includes various assist features to enhance the qualityand/or resolution of imaging during a photolithography process, in whichthe integrated circuit pattern is transformed to a substrate such as asemiconductor wafer. For example, a plurality of features areincorporated into the mask pattern and configured approximate anintegrated circuit feature to compensate for optical proximity errorusing an optical proximity correction (OPC) technology. These featuresare also referred to as OPC features.

In one embodiment, the OPC features includes scattering bars 214 asillustrated in FIG. 2 a. Scattering Bars are a proven and effective OPCtechnique that enhance wafer imaging performance for current and futuretechnology nodes. Scattering bars can be sub-resolution features thatare placed on a mask next to isolated lines and semi-isolated lines,enabling them to image like the dense lines.

In another embodiment, the OPC features include other assist features,such as serifs and hammerheads, for line-end treatment such as features216 illustrated in FIG. 2 a. Two related optical proximity effects areline end shortening and corner rounding, where the ends of lines tend toshrink from where the design specifies, and square corners on the maskare imaged as round corners on the wafer. Line-end treatment, such as inthe form of serifs and hammerheads, stretches out the ends of lines onthe mask so that the final imaged lines have the desired length, andsharp corners.

The OPC features may also include other suitable features to reduce theoptical proximity effect. For example, due to the optical proximityeffect, equal width lines image differently at different pitches, andisolated lines image differently than dense lines. Line biasing adjuststhe width of lines on the reticle to compensate for this variation ofline width across pitch. In another embodiment, OPC or other maskfeatures may be incorporated into the mask pattern (mask layout) tocompensate for the global pattern loading effect.

In another embodiment, the mask pattern may include dummy featuresincorporated into the integrated circuit features. For example, FIG. 2 bshows a top view of an exemplary mask pattern 220 having variousintegrated circuit features 222, 224 and 226. The mask pattern 220 alsoincludes a plurality of dummy features 228 configured approximate theintegrated circuit features. In one embodiment, the dummy features areused to enhance a chemical mechanical polishing (CMP) process. For thispurpose in one example, the dummy metal features are designed andincorporated into damascene structure to make pattern density moreuniform to improve the planarization process. In other embodiments, thedummy features are used to improve pattern density, reduce deviations(e.g., “dishing”) from a flat profile, and/or reduce etching loadingeffects.

The mask patterns may be formed on one or more absorption layers coatedon the mask substrate 110. An absorption layer may include chromium(Cr), MoSi, and/or other suitable materials in various embodiments. Theabsorption layer is coated on the mask substrate and is then patternedto form the mask pattern.

In another embodiment, the mask pattern may at least partially includephase shift features, which is referred to as a phase shift mask (PSM).The mask pattern may be formed on one or more phase shift materiallayers coated on the mask substrate 110. For example, a phase shiftmaterial layer may also be an absorption layer and the phase shiftmaterial layer includes MoSi. In another embodiment, the phase shiftmaterial layer may be a transparent material coated on the masksubstrate, and the phase shift layer includes silicon oxide. In anotherembodiment, the phase shift material layer includes a portion of thetransparent mask substrate. For example, the mask pattern of the PSM isformed in the transparent fused quartz substrate.

A method to write the mask pattern to the mask may include resistpatterning and etching processes. After a coated resist layer ispatterned according to the designed mask pattern, an etching process isimplemented to partially remove an underlying layer to transfer theresist pattern thereto. The underlying layer includes a coatedabsorption layer, a coated phase shift layer, and/or the transparentsubstrate. In the patterning process, the designed mask pattern iswritten on the absorption layer using a mask writing technique such ase-bean writing. Other writing methods such as ion beam writing mayalternatively be used to form the mask pattern. During the etchingprocess, etching rate and etching behavior may depend on a globaletching pattern density, referred to as the global etching loadingeffect. The pattern density can be defined as the relative patternedfeature areas. The global etching loading effect results in patterndimension variation (or CD variation). For example to illustrate this,if a pattern feature at 30% pattern density targets 100 nm width afterthe etching process, then the same pattern at 20% pattern density mayachieve 95 nm width and the same pattern at 40% pattern density mayachieve 105 nm width. The CD variation relative to the ideal CD may bereferred to as the global etching bias (or global loading bias).Generally, in addition to the global etching loading effect, a globalpattern loading effect may also include other effects such as foggingeffect during e-beam (EB) writing, and proximate effect. Although mostexamples in the disclosure are about the etching process, otherprocesses such as EB writing and associated global effect may also beincluded and considered in the method 100 without departure of thespirit of the present disclosure. For simplicity, the etching process isdescribed and illustrated here. The etching process may also includemicro-loading effect associated with local pattern densities.

During the step 112 of writing a mask pattern to the mask 200, a dosemap is implemented to tune local writing dose (energy) to compensatevarious loading effects and/or other location-dependent variations. Inone example, the e-beam radiation duration on one spot is shortened orprolonged to vary the dose. In another embodiment, the e-beam intensityprojected on one spot is tuned higher or lower to vary the dose.Referring to FIG. 3 a, a mask 230 includes two regions 232 and 234 withdifferent global densities. For example, the first region 232 has aglobal pattern density about 20% and the second region 234 has a globalpattern density about 80%. The critical dimension (CD) over variousdoses can be found out through experiments such as an exemplary CD vs.dose diagram 244 illustrated in FIG. 3 c. The doses for various globalregions can be determined by using the CD vs. dose diagram. For example,the dose for the first region 232 can be extracted from the CD vs. dosediagram according to the global pattern density in the first region 232and the associated global loading bias. The loading bias can also beobtained experiments. Thus obtained dose is assigned to the first region232. Similarly, the dose for the second region 234 can also be extractedfrom the CD vs. dose diagram according to the global pattern density inthe second region 234 and the associated global loading bias. That doseis assigned to the second region 234. Thus, a set of global doses forvarious regions can be determined and are referred to as a global dosemap. The size of the global region cab be chosen. The global dose mapcan be used to implement the mask writing process with locationdependent dose to compensate the global loading effect.

Referring to FIG. 3 b, a local dose map may also be similarly used. Amask 240 is divided into a plurality of regions 242, each region havingits own local pattern density. The doses for various regions can befound out using the CD vs. dose diagram such as the CD vs. dose diagram244. For example, the dose for one particular region can be extractedfrom the CD vs. dose diagram according to the associated pattern densityto that particular region and the associated loading bias. Thus obtaineddose is assigned to that particular region. Repeat the same procedureuntil the all regions 242 are exhausted. Thus, a set of doses mapping tothe plurality of regions 242 are determined and are referred to as alocal dose map. The size of the global region cab be properly chosen.This dose map can be used to implement the mask writing process withlocalized dose to each region to compensate the local loading effect. Inone embodiment, the local dose map and global dose map can be combinedinto one dose map to reduce both global and local loading effects.

The mask making (or mask writing) tool, such as an e-beam writing tool,for mask writing process can be designed to include a dose map moduleand enable a dose map for mask writing process. For example, the writingtool is designed to determine the dose map for a mask pattern based themask pattern, loading bias data, and the CD vs. dose diagram. Infurtherance of the example, the dose map is saved in a database of thewriting tool and is used to vary the dose from region to regionaccordingly during a writing process to form the mask pattern on a mask.The plurality of regions may be divided into different sizes dependingon the criticality of each region.

Referring to FIGS. 1-2 and 4-6, the method 100 proceeds to step 112 byinspecting the plurality of mask pattern features formed on the mask.The mask inspecting process aims to identify mask defects for maskrepair and enhancing mask fabrication yield. The inspecting process atthis step utilizes multiple inspection criteria. As described above ofFIGS. 2 a and 2 b, the mask pattern include various pattern featuresincluding integrated circuit features (main features), assist features,and dummy features. Each feature has its own sensitivity due todifferent criticalities to the mask pattern. For example, the mainfeatures are more sensitive to CD variation and need to be inspectedwith stringent criteria. In another example, the assist patterns may beless sensitive relative to the main features and need to be inspectedusing loose criteria. In another example, the dummy patterns may be muchless sensitive relative to the main features and need to be inspectedusing even more loose criteria. The existing mask inspection processuses one criterion to inspect the all mask features, resulting falsefailure, high manufacturing cost (high inspection cost and highrepairing cost) and low throughput.

In one embodiment, the multiple sensitivity inspecting process includessetting up pixel size (e.g., the size of a region) and threshold (e.g.,inspection pass/fail criteria). Small pixel size may result in highinspection cost. Large pixel size may result in degraded inspectionperformance. Proper pixel size can be chosen based on the above twofactors and/or other relevant factors. Each pixel may have differentsize and/or shape based on the sensitivity (or criticality) of eachparticular region and pattern features in that region. The threshold foreach region (pixel) is chosen differently, more stringent or loosedepending on the criticality of the region and pattern features in thatregion.

The sensitivity is not only related to the type of features but alsorelated to the device performance. Further, the sensitivity is relatedto the relationship between that feature and other features in the sameregion in an approximate layer when the mask pattern is transferred to asemiconductor wafer, and the criticality of the relationship. Forexample, FIG. 5 illustrates a pattern 270 formed on different masks andto be transferred the different layers in the same region of thesemiconductor wafer. The pattern 270 includes a feature 272 and anotherfeature 274. The mask pattern 270 also includes an overlap region 276.In one example for illustration, the pattern feature 272 is a feature tobe formed in the polysilicon layer. The pattern feature 274 defines anactive region in the semiconductor wafer. The overlap region 276 is moresensitive and needs a more stringent criteria during the mask inspectionprocess. In furtherance of the example, the regions 272, 274, and 276may have different sensitivities and therefore be assigned withdifferent thresholds.

FIG. 4 is an exemplary block diagram of a multiple sensitivityinspection module 250, in one embodiment, constructed according toaspects of the present disclosure. The plurality pattern features in amask pattern can be categorized into various sensitivity groups 252,254, 256, 258 and so on. Each sensitivity group has its own pixeldimensions and inspection threshold. For example, the sensitivity group252 has its pixel and threshold defined as pixel A and threshold A,respectively. The sensitivity group 254 has its pixel and thresholddefined as pixel B and threshold B, respectively. The sensitivity group256, pixel C and threshold C, and so on.

Referring to FIGS. 6 a through 6 d as top views of an exemplary maskpattern in one embodiment, categorization of the pattern features withdifferent sensitivities is described for illustration. The mask pattern280 in FIG. 6 a includes a contact feature 282 and various scatteringbars 284 and 286 positioned approximate the contact feature. In existinginspection procedures, all pattern features have one threshold settingwith no differentiation. According to the present disclosure, eachfeature may be classified to a different sensitivity group and assignedwith a different threshold. In one embodiment, the sensitivity (and/orthreshold) may be represented by a data type and/or a data layer of aGDS document. GDS is a binary format for a mask layout tapeout. The GDSformat includes a data layer and a data type (Data layer and data typeare collectively referred to as data type whenever proper forsimplicity). For example, the contact feature in GDS format may includea data layer as 31 and a data type 0 (gds: 31,0). Since the data typeand data layer each has multiple values, they can be used to present thethreshold of the pattern feature. In furtherance of the example, thecontact feature 282 is categorized into a first sensitivity group, asillustrated in FIG. 6 b and is represented by the data type 0. Thescattering bars 284 are categorized into second sensitivity group, asillustrated in FIG. 6 c and are represented by the data type 1. Thescattering bars 286 are categorized into third sensitivity group, asillustrated in FIG. 6 d and are represented by the data type 2. Infurtherance of this example, if sensitivity is measured by 1 to 100 withhighest sensitivity at 100. The contact feature 282 may be assigned witha sensitivity at 1of as an example. The scattering bars 284 may beassigned with a sensitivity of 90. The scattering bars 286 may beassigned with a sensitivity of 80.

FIG. 7 a illustrates a structure 290 having a polysilicon features 292and active region features 294 formed in different masks. When thepolysilicon features 292 have a data layer 17 and a data type 0 (gds:17,0) while the active region features have a data layer 6 and a datatype 0 (gds: 6, 0). The overlap region between the polysilicon features292 and the active region features 294 have a different sensitivity thatcan be determined through an AND logic operation of “(6, 0) and (17,0)”, resulting in the gds: (50, 1). The sensitivity of polysiliconfeatures that are not overlapped with the active region can bedetermined by a NOT logic operation of “(17, 0) not (6, 0)”, resultingin the gds: (50, 2). Therefore, the overlapped region has a differentsensitivity than that of non-overlapped polysilicon regions. FIG. 7billustrates a plurality of dummy features 298. The gds data for thedummy features 298 may be (50, 0).

The inspection tool used to inspect the mask pattern written on the maskincludes a customized sensitivity module to enable multiple sensitivityinspections of the mask pattern. The customized sensitivity moduleintegrated with the inspection tool enables set up and inspection ofthresholds and/or pixels, and also enables a two or more layersinspection process in which each pattern feature is determined of itssensitivity, considering multiple layers. The mask inspecting processincludes utilizing an aerial image measurement system (AIMS) in oneembodiment.

Referring again to FIG. 1, the method proceeds to step 116 by repairingthe defects of the mask identified at the previous mask inspection step.The mask repairing process implements different accuracies to variouspattern features according to their particular sensitivities. Variousrepairing tools are implemented to repair different pattern featuresaccording to their sensitivities. In one embodiment, different pixel mayrequest different repairing tool. The less sensitive feature with largepixels may use less accurate repairing tool.

Referring to FIG. 4, the sensitivity group 252 uses the repairing rule262 and associated repairing tools for repairing, and uses aerial imagemeasurement system (AIMS) for imaging verification/check/inspection. Thesensitivity group 254 uses repairing rule 264, and so forth. In oneembodiment, the various repairing tools include e-beam repairing tool,atomic force microscope (MSF) micromachine, focused ion beam, and laserbeam, each having a different accuracy. For example, the patternfeatures in the sensitivity group 252 may use e-beam repairing tool formask repairing. The pattern features in the sensitivity group 254 mayuse AFM micromachine for mask repairing. The pattern features in thesensitivity group 256 may use focused ion beam for mask repairing. Thepattern features in the sensitivity group 258 may use laser beam formask repairing.

Thus, the present disclosure provides a method for making a mask. In oneembodiment, the method includes writing a plurality of pattern featureson the mask; inspecting the plurality of pattern features with differentinspection sensitivities; and repairing the plurality of patternfeatures on the mask according to the inspecting of the plurality ofpattern features. The method may further include assigning differentdata types and data layers, or various combinations thereof (orcollectively referred to as data types) to the plurality of patternfeatures, to present the different inspection sensitivities.

In the method, the plurality of the pattern features may include a firstpattern feature associated with a first inspection sensitivity; and asecond pattern feature associated with a second inspection sensitivitylower than the first inspection sensitivity. The first pattern featuremay include a device feature (an integrated circuit feature). The secondpattern feature may include one element selected from the groupconsisting of an optical proximity correction (OPC) feature and a dummypattern. The first pattern feature may include an association with atleast one pattern layer to be formed on another mask and transferred toan adjacent layer on a semiconductor substrate.

The repairing of the plurality of pattern features may include repairingthe first pattern feature using a first repairing accuracy; andrepairing the second pattern feature using a second repairing accuracylower than the first repairing accuracy. The repairing of the pluralityof pattern features may include repairing each of the plurality ofpattern features using one repairing tool selected from the groupconsisting of e-beam repairing tool, atomic force microscope (AFM)micromachine, focused ion beam tool and laser beam tool, according to anassociated repairing accuracy. The inspecting of the plurality ofpattern features may include utilizing an aerial image measurementsystem (AIMS). The writing of the plurality of pattern features mayinclude writing each of the plurality of pattern features using a doseaccording to a loading factor dose map associated to the mask.

The present disclosure also provides a mask making tool. In oneembodiment, the inspection tool includes a sensitivity module designedto assign pattern features to different data types, each associated withone of a plurality of sensitivities; and an inspection unit designed torepair the pattern features according to associated sensitivities.

In the mask inspection tool, each of the plurality of sensitivities maybe characterized by at least one of threshold and pixel. The sensitivitymodule may be operable to assign a pattern feature with one of theplurality of sensitivities according to performance criticality of thepattern feature. The repairing unit may include one selected from thegroup consisting of e-beam repairing tool, atomic force microscope (AFM)micromachine, focused ion beam tool and laser beam tool.

The present disclosure also provides a mask making system. In oneembodiment, the mask making system includes a mask writing unit designedto write pattern features on a mask; and a loading factor dose moduledesigned to assign one of the pattern features with a particular doseaccording to a loading factor dose map.

The present disclosure also provides another mask making system. In oneembodiment, the mask making system includes a loading factor dose moduledesigned to assign pattern features with various doses according to aloading factor dose map; a mask data module designed to associate thepattern features with different data types according to assigned doses;and a mask writing unit designed to write the pattern features accordingto associated data types.

In various embodiments of the disclosed mask making system, the maskmaking system may further include a mask inspection unit designed forinspecting according to various inspection sensitivities. The maskmaking system may further include a mask repairing unit designed forrepairing the pattern features using various repairing accuracies. Theparticular dose may be assigned further based on layout proximity factorof the pattern features. The loading factor dose module may be operableto provide a first dose map readable by the mask writing unit and asecond dose map readable by an engineer.

In various embodiments, a plurality of pattern features are assignedwith different data types and/or different data layers (or collectivelyreferred to as different data types) to represent different writingdoses, different inspection sensitivities, different repairingaccuracies, or combinations thereof. Therefore, the mask making systemand method can perform a writing with a particular dose, an inspectionwith a particular sensitivity, and/or a repairing process with aparticular accuracy according the assigned data type.

Although embodiments of the present disclosure have been described indetail, those skilled in the art should understand that they may makevarious changes, substitutions and alterations herein without departingfrom the spirit and scope of the present disclosure. Accordingly, allsuch changes, substitutions and alterations are intended to be includedwithin the scope of the present disclosure as defined in the followingclaims. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents, but also equivalent structures.

1. A method for making a mask, comprising: assigning a plurality ofpattern features to different data types; writing the plurality ofpattern features on a mask; inspecting the plurality of pattern featureswith different inspection sensitivities according to assigned datatypes; and repairing the plurality of pattern features on the maskaccording to the inspecting of the plurality of pattern features.
 2. Themethod of claim 1, wherein the plurality of the pattern featurescomprises: a first pattern feature associated with a first inspectionsensitivity; and a second pattern feature associated with a secondinspection sensitivity lower than the first inspection sensitivity. 3.The method of claim 2, wherein the first pattern feature comprises adevice feature.
 4. The method of claim 2, wherein the second patternfeature comprises one element selected from the group consisting of anoptical proximity correction (OPC) feature and a dummy pattern.
 5. Themethod of claim 2, wherein the first pattern feature includes anassociation with at least one pattern layer to be formed on another maskand to be transferred to an adjacent layer on a semiconductor substrate.6. The method of claim 2, wherein the repairing of the plurality ofpattern features comprises: repairing the first pattern feature using afirst repairing accuracy; and repairing the second pattern feature usinga second repairing accuracy lower than the first repairing accuracy. 7.The method of claim 6, wherein the repairing of the plurality of patternfeatures comprises repairing each of the plurality of pattern featuresusing one repairing tool selected from the group consisting of e-beamrepairing tool, atomic force microscope (AFM) micromachine, focused ionbeam tool and laser beam tool, according to an associated repairingaccuracy.
 8. The method of claim 1, wherein the inspecting of theplurality of pattern features comprises utilizing an aerial imagemeasurement system (AIMS).
 9. The method of claim 1, where the writingof the plurality of pattern features comprises writing each of theplurality of pattern features using a dose according to a loading factordose map associated to the mask.
 10. A mask making tool, comprising: asensitivity module designed to assign pattern features to different datatypes, each associated with one of a plurality of sensitivities; and aninspection unit designed to repair the pattern features according toassociated sensitivities; wherein each of the plurality of sensitivitiesis characterized by at least one of threshold and pixel.
 11. The maskmaking tool of claim 10 wherein at least one pattern is an opticalproximity correction pattern.
 12. The mask making tool of claim 10,wherein the sensitivity module is operable to assign a pattern featurewith one of the plurality of sensitivities according to a criticalperformance of the pattern feature.
 13. The mask making tool of claim10, wherein a sensitivity module is designed to assign the patternfeatures to different data layers, each associated with one of aplurality of sensitivities.
 14. The mask making tool of claim 10,further comprising a repairing unit selected from the group consistingof e-beam repairing tool, atomic force microscope (AFM) micromachine,focused ion beam tool and laser beam tool.
 15. A mask making system,comprising: a loading factor dose module designed to assign patternfeatures with various doses according to a loading factor dose map; amask data module designed to associate the pattern features withdifferent data types according to assigned doses; and a mask writingunit designed to write the pattern features according to associated datatypes.
 16. The mask making system of claim 15, wherein the loadingfactor dose module is operable to provide a first dose map readable bythe mask writing unit and a second dose map readable by an engineer. 17.The mask making system of claim 15, further comprising a mask inspectionunit designed for inspecting the pattern features according to variousinspection sensitivities.
 18. The mask making system of claim 17,wherein the mask data module is designed to further assign each of thevarious inspection sensitivities to a particular data type.
 19. The maskmaking system of claim 15, further comprising a mask repairing unitdesigned for repairing the pattern features using various repairingaccuracies.
 20. The mask making system of claim 15, wherein the variousdoses are assigned further according to a layout proximity factor of thepattern features.